Common aperture antennas are generally known. For example, U.S. Pat. No. 5,214,438 describes a millimeter wave and infrared sensor in a common receiving aperture. In the past, false target acquisitions have degraded the cost effectiveness of single sensor seekers. Weather conditions and the time of day can adversely affect the ability of the sensor to acquire the target. Millimeter wave (MMW) energy is useful under adverse weather conditions. However, the resolution is not as precise as exhibited by optical systems operating in the infrared (IR) region. In an optical system, resolution is adversely affected by rain, fog or humidity. These conditions can reduce the effectiveness of such sensors in the optical spectral region. Target acquisition can be substantially improved by combining millimeter wave and infrared optical signals, substantially reducing the influence of climatic conditions. IR and MMW are also susceptible to known countermeasures of various kinds and therefore a combined aperture system is less susceptible to a single type of countermeasure.
Despite the aforementioned advantages associated with such common aperture antennas, applicants have found that various problems exist with conventional designs. For example, a prime-focus reflector antenna design may have an abnormally large amount of central blockage (much larger than the feed would normally induce) created by another part of the overall system. In such a situation, it is left to the antenna designer to maximize the reflector antenna performance in the presence of this blockage.
As a more specific example, an IR sensor within the common aperture antenna may share the same main reflector surface as an RF (microwave or millimeter wave) reflector antenna. In such a situation, the reflector configuration is often dictated by the more stringent IR system requirements. This typically has an adverse affect on the performance of the RF system. That is to say what is advantageous for the IR system is typically not what is advantageous for the RF system.
In view of the aforementioned shortcomings associated with conventional designs, there is a strong need in the art for a common aperture antenna which can provide efficient operation with respect to each of the systems. For example, there is a strong need for a common aperture reflector antenna which may be optimized for an IR system and also efficiently configured for an RF system. Moreover, there is a strong need in the art for a method of designing such an antenna.